This invention relates to the Joining and bonding of articles, and, in particular, to a diffusion welding process.
The need to mechanically, electrically, or thermally join articles or pieces together arises in a wide range of situations, and many techniques have been developed. In the manufacture of microelectronic devices, for example, it is often necessary to mechanically and/or electrically bond terminals together, and to mechanically bond substructures together. The bonding must be accomplished without damaging the microelectronic devices already present.
The most common approach to such bonding requirements in microelectronic devices is to solder the pieces together. In soldering, a pure metal or alloy having a low melting temperature is provided at the locations to be Joined. Lead-tin, lead-indium, and indium solders are widely used. Lead-tin solder is the familiar solder available in hardware stores, and the other solders are made for more specialized applications. The solder and surrounding regions to be joined are heated to a temperature sufficient to melt the solder and cause it to flow over the surfaces to be Joined. The heating is removed, and the parts are allowed to cool. As the parts cool, the solder solidifies to Join the parts together.
Soldering is widely used, but has drawbacks in some applications. In order to cause the solder to wet and flow over the surfaces to be bonded, it is usually necessary to utilize a flux that cleans the surfaces to be bonded before the solder melts. Fluxes are often corrosive compositions that clean the surface, but also leave a residue that can cause long-term damage to the microelectronic components. It may also be necessary to acid etch the surfaces to be bonded before soldering begins, to improve the adherence of the solder to the surface. The acid used in the etching may similarly lead to damage of the microelectronic device. Also, there are no known low-temperature solders suitable for microelectronic applications that have high strengths after bonding. Careful process control is required to achieve a good solder bond, including use of the correct temperature and atmosphere conditions. Finally, even with careful selection of the solder, proper surface preparation of the parts to be bonded, and close process control, there may be gaps or holes in the final solder Joint that greatly reduce its strength.
Soldering is expected to remain a viable Joining technique for many applications. In others, these drawbacks cause the technique to be less than satisfactory. There is a need for an improved Joining technique that can replace soldering in such applications. The present invention fulfills this need, and further provides related advantages.